Method sync

imperative/src/impl/persistent_cache.cpp:121–124

    uint64_t m_timeout;

    void sync() {
        m_client.sync_commit<double, std::milli>(std::chrono::milliseconds(m_timeout));
        mgb_assert(valid());
    }
};

class ExtendedInFilePersistentCache final : public ExtendedPersistentCache {